南海西沙永乐龙洞沉积物组成、来源及其沉积作用     

范德江  田元  傅亮  罗珂  孙晓霞  毕乃双  姚鹏  刘光兴  陈洪举  杨作升 《海洋与湖沼》2018,49(6):1203-1210

南海永乐龙洞发育于永乐珊瑚礁台地,龙洞深度达300m,为世界之最。沉积物堆积在龙洞的洞壁斜坡、龙洞中部的转折平台以及洞底等部位。使用激光粒度仪、X射线粉晶衍射仪、X射线荧光光谱仪等对采自不同深度的沉积物进行了粒级、矿物物相、元素含量的研究。研究结果表明:龙洞沉积物绝大部分为钙质生物碎屑,以砂粒级碎屑为主,含砾石碎屑、粉砂碎屑,分选和磨圆差;沉积物矿物组成以文石、高镁方解石为主,含少量低镁方解石,其平均含量分别为69%、28%、3%;化学组成以Ca、Mg、Sr为主,平均含量分别为35.5%、0.9%、0.5%,含少量Si、Al、Ti、P、S等元素。该区沉积物来源包括礁坪生物碎屑和东亚季风风尘陆源物质两个方面,以礁坪来源的生物碎屑为主;龙洞沉积作用包括机械捕获作用和垂直沉降作用两种方式,而以机械捕获作用为主。  相似文献   

Downvalley fining of hillslope sediment in an alpine catchment: implications for downstream fining of sediment flux in mountain rivers     

Leonard S. Sklar  Clifford S. Riebe  Jennifer Genetti  Shirin Leclere  Claire E. Lukens 《地球表面变化过程与地形》2020,45(8):1828-1845

The size distributions of sediment delivered from hillslopes to rivers profoundly influence river morphodynamics, including river incision into bedrock and the quality of aquatic habitat. Yet little is known about the factors that influence size distributions of sediment produced by weathering on hillslopes. We present results of a field study of hillslope sediment size distributions at Inyo Creek, a steep catchment in granitic bedrock of the Sierra Nevada, USA. Particles sampled near the base of hillslopes, adjacent to the trunk stream, show a pronounced decrease in sediment size with decreasing sample elevation across all but the coarsest size classes. Measured size distributions become increasingly bimodal with decreasing elevation, exhibiting a coarse, bouldery mode that does not change with elevation and a more abundant finer mode that shifts from cobbles at the highest elevations to gravel at mid elevations and finally to sand at low elevations. We interpret these altitudinal variations in hillslope sediment size to reflect changes in physical, chemical, and biological weathering that can be explained by the catchment's strong altitudinal gradients in topography, climate, and vegetation cover. Because elevation and travel distance to the outlet are closely coupled, the altitudinal trends in sediment size produce a systematic decrease in sediment size along hillslopes parallel to the trunk stream. We refer to this phenomenon as ‘downvalley fining.’ Forward modeling shows that downvalley fining of hillslope sediment is necessary for downstream fining of the long-term average flux of coarse sediment in mountain landscapes where hillslopes and channels are coupled and long-term net sediment deposition is negligible. The model also shows that abrasion plays a secondary role in downstream fining of coarse sediment flux but plays a dominant role in partitioning between the bedload and suspended load. Patterns observed at Inyo Creek may be widespread in mountain ranges around the world. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

基于几何形态测量学的四种滨螺形态差异与系统发生关系研究   总被引：1，自引：0，他引：1  

陈楠桦  梁仁杰  白义  王海瑞 《海洋与湖沼》2018,49(6):1365-1374

运用几何形态测量学方法研究浙江省大陈岛海域常见的4种滨螺间的形态关系。对4种滨螺的壳口、螺体分别进行数字化标点,经叠印分析、主成分分析(PCA)和薄片样条法分析,获得4种滨螺在壳口和螺体上的差异,并进一步分析其形态特征与潮间带环境适应性关系。PCA结果表明四种滨螺壳口间差异在主成分轴上无法有效分开,而螺体间差异在主成分轴上能有效分开,说明壳口特征在不同滨螺间不具有规律性差异。螺体的PCA中PC1轴可以将短滨螺与其他3种滨螺区分,薄片样条法分析显示差异的部位主要在体螺层的宽度和螺体的高度间,PC2轴可以将粒结节滨螺与其他3种滨螺分开,薄片样条法分析显示差异部位主要是体螺层之上第一层以及体螺层之间。基于螺体特征的4种滨螺亲缘关系分析表明粗糙滨螺与塔结节滨螺亲缘关系最近,其次为短滨螺,粒结节滨螺最不相近。运用特征追踪法对螺层和螺肋特征追踪,结果表明螺层6层,螺肋密生是滨螺的祖先特征,后来演化出7层和8层的螺层特征以及颗粒状突起的螺肋特征。  相似文献   

Helmert方差分量估计在GPS/GLONASS/BDS组合定位权比确定中的应用     

刘金海  涂锐  张睿  张鹏飞  卢晓春 《大地测量与地球动力学》2018,38(6):568-570

因GNSS系统间观测噪声、轨道精度的差异，采用经验权比进行组合定位难以得到最优结果。基于此，在GPS/GLONASS/BDS组合定位中引入Helmert方差分量估计，对GPS/GLONASS/BDS组合单点定位和基线解算中各系统观测值进行合理定权。实验表明，采用该方法确定的伪距观测值最佳权比为5∶1∶1，相位观测值最佳权比为1∶1∶1，有效提高了GPS/GLONASS/BDS组合定位的精度和可靠性。  相似文献   

生态最相关水文指标的优选及其在洞庭湖环境流量估算中的应用     

程俊翔  徐力刚  姜加虎 《湖泊科学》2018,30(5):1235-1245

水文改变指标(IHA)能够较为全面地描述水文状况,在评估水文情势改变及其生态系统影响方面具有广泛的应用.尽管该指标体系较为完善,但是数量众多的水文变量仍然存在信息冗余问题.根据洞庭湖城陵矶水文站1955-2014年的径流量数据,采用主成分分析(PCA)筛选了生态最相关水文指标(ERHIs),结合ERHIs改进了用于估算环境流量的变化范围法(RVA),并将其应用在洞庭湖出口的环境流量估算中.基于PCA选取了年最大90日流量、年最小3日流量、年最小流量出现时间、3月流量、6月流量、流量逆转次数和低流量年内平均历时7个变量作为洞庭湖出口的ERHIs.纵向和横向的对比分析都表明选取的ERHIs是合理的.ERHIs不仅有效缓解了IHA的冗余性问题,还有利于抓住最关键的生态水文变量.根据ERHIs改进的RVA方法在设定洞庭湖出口环境流量时,极大地简化原来的众多管理目标,对生态水文研究、水资源管理和生态保护都具有重要的参考价值和借鉴意义.  相似文献   

2012年江苏扬州M 4.9地震前地磁垂直分量日变双低点异常     

郭明瑞  胡久常  吴佳林  王桂丹  王锡娇  崔泽岩 《地震地磁观测与研究》2018,39(3):89-93

2012年6月13日和7月10日华东地区部分地磁台垂直分量日变形态出现双低点异常，首次异常出现后37天，于7月20日发生江苏扬州M 4.9地震，震中位于低点位移分界线附近。分析认为，在强震前由于应力变化，引起孕震体环境中介质电导率等电磁性质发生改变，区域地磁场垂直分量日变曲线出现相位和幅度变化，说明地磁垂直分量日变双低点异常与地震的孕育和发生相关。  相似文献   

Chemical Procedures for Rhenium Extraction from Geological Samples: Optimising the Anion Resin Bead Clean‐up Step     

Gang Yang  Aaron Zimmerman  Nicole C. Hurtig  Svetoslav V. Georgiev  Vineet Goswami  Judith L. Hannah  Holly J. Stein 《Geostandards and Geoanalytical Research》2020,44(2):231-242

Rhenium–osmium geochronometry for samples with low Re and complex matrices requires improved Re extraction methods. Here, we investigate plausible controls on efficiency and efficacy of Re extraction during our anion resin bead purification. Four different protocols are compared, each isolating a single variable to test. Rhenium concentrations for solutions at each step of each protocol document differences in chemical recovery/yield. The negative‐thermal ionisation mass spectrometry (N‐TIMS) signal intensity serves as a proxy for Re yield and purity. These data document correlations between the N‐TIMS signal intensity and (a) the duration of anion resin bead conditioning prior to loading with Re‐bearing solution, and (b) both duration and strength of nitric acid used during rinsing of the Re‐loaded anion resin bead. The optimal protocol improved Re signal intensity around fourteen times compared with our current Re extraction protocol, an aggregate of 2.4 times improvement in chemical recovery (yield) and 5.8 times improvement in emission efficiency (purity). Repeated N‐TIMS isotopic measurements on our in‐house Re standard solution (1407) verify that our optimal protocol‐3 does not fractionate Re isotopes. The improved anion resin bead method considerably lowers the Re detection limit and allows Re‐Os isotopic analysis of picogram‐level Re hosted in geological samples with complex matrices.  相似文献   

化学刺激法提高花岗岩类岩石裂隙渗透性的实验研究     

郭清海  何曈  庄亚芹  骆进  张灿海 《地学前缘》2020,27(1):159-169

增强型地热系统(EGS)用于通过人工形成地热储层的方法从深部低渗透性岩体中开采地热能;国际上常采用水力压裂辅以化学刺激的方法改造EGS 储层以提高其渗透率。本文以采自青海共和盆地的花岗闪长岩样品为对象,选用3种不同化学刺激剂(氢氧化钠、盐酸和土酸),在3组不同注入流速条件下开展了系统化学刺激实验。结果表明:注入盐酸和土酸后样品渗透率均有提高,且采用土酸时渗透率提高幅度明显大于盐酸;但注入氢氧化钠后,样品渗透率反而降低。在3类化学刺激剂中,土酸对长石类矿物的溶蚀能力最强,而氢氧化钠溶液对石英的溶蚀能力最强,但氢氧化钠溶液在溶解岩石样品裂隙表面矿物后极易形成非定形态二氧化硅或非定形态铝硅酸盐蚀变矿物并阻塞裂隙,反而对化学刺激效果造成负面影响。总体来看,土酸是青海共和盆地干热岩体的最佳化学刺激剂。在中等注入速度(3 mL·min^-1)条件下,土酸对岩石样品的溶蚀程度就可达到最高;在此基础上进一步降低流速,则可能使溶解组分更易从液相中沉淀而充填于样品裂隙,导致样品渗透率有所下降。  相似文献   

2013年岷县—漳县6.6级地震地磁垂直分量日变化低点时间空间分布特征     

戴勇  高立新  姚丽  朱培育  格根  王磊 《地震》2019,39(3):106-114

2013年6月16日, 中国大陆西部出现地磁低点位移。 异常出现后一个月内, 位于低点位移分界线附近发生7月22日岷县、 漳县交界6.6级地震。 本文通过采用实测低点时间减去理论低点时间的方法剔除低点时间经度效应, 并以剔除经度效应后低点时间为0 h的等值线作为低点位移分界线, 2013年岷县—漳县6.6级地震震中处于6月16日地磁低点位移分界线上。 对异常期间的中国大陆地区地磁垂直分量日变形态进行统计, 发现其存在显著的分区特征, 低点时间为正的区域内日变化形态基本呈现W型, 低点时间为负的区域内日变化形态主要呈现V字型特征。 低点位移异常日期间, 中国大陆存在显著的高梯度带, 本文采用梯度值定量描述低点时间空间变化程度。 在6月13日正常日期间, 中国大陆地区未出现梯度值大于1.5 h/(°)的区域, 在6月16日异常日期间, 出现梯度值大于1.5 h/(°)的区域, 2013年岷县—漳县6.6级地震位于高梯度区边缘。  相似文献   

Modeling spatially correlated spectral accelerations at multiple periods using principal component analysis and geostatistics     

《地震工程与结构动力学》2018,47(5):1107-1123

Regional seismic risk assessments and quantification of portfolio losses often require simulation of spatially distributed ground motions at multiple intensity measures. For a given earthquake, distributed ground motions are characterized by spatial correlation and correlation between different intensity measures, known as cross‐correlation. This study proposes a new spatial cross‐correlation model for within‐event spectral acceleration residuals that uses a combination of principal component analysis (PCA) and geostatistics. Records from 45 earthquakes are used to investigate earthquake‐to‐earthquake trends in application of PCA to spectral acceleration residuals. Based on the findings, PCA is used to determine coefficients that linearly transform cross‐correlated residuals to independent principal components. Nested semivariogram models are then fit to empirical semivariograms to quantify the spatial correlation of principal components. The resultant PCA spatial cross‐correlation model is shown to be accurate and computationally efficient. A step‐by‐step procedure and an example are presented to illustrate the use of the predictive model for rapid simulation of spatially cross‐correlated spectral accelerations at multiple periods.  相似文献